Power hydraulic brake device



Aug- 28, 1962 R. E. SCHWARTZ ETAL 3,050,944

POWER HYDRAULIC BRAKE DEVICE Original Filed March 28, 1955 2Sheets-Sheet 1 V3 ln S; :g n m ug- 28, 1962 R. E. SCHWARTZ ETA.3,050,944

POWER HYDRAULIC BRAKE DEVICE 2 Sheets-Sheei'. 2

Original Filed March 28, 1955 KM. u Y JL M f n W [MM w 3,050,944 PWERHYDRAULIC BRAKE DEVICEI Robert E. Schwartz, Clayton, Mo., Roy P. Stahl,South Bend, ind., and Edward J. Falk, St. Louis, Mo., assignors to'Wagner Electric Corporation, St. Louis, Mo., a corporation of DelawareContinuation of abandoned application Ser. No. 496,711, 23, 1955. Thisapplication Nov. 22, 1960, Ser. No. 71,102

13 Claims. (Cl. 60-54.6)

This invention relates to series power hydraulic braking systems and inparticular to a servo motor employed therein to control said system.

One of the principal objects of the present invention is to provide aservo motor which is balanced to function regardless of the existingambient pressure in its particular `section of the system.

Another object of this invention is to provide a servo motor whichoperates the vehicle brake assemblies even if there is a power failurein the system.

Still another object of the present invention is to provide a servomotor having a free and slidably mounted power piston which does notdisplace pressure fluid during a braking operation after there has beena power failure and which thereby reduces Vthe manually applied forcenormally required under such conditions. i

Still another object of the present invention is to provide a servomotor which provides feel for the operator. Feel is the proportionalreactionary force in opposition to the applied force which affords theoperator an appraisal as to the extent of the braking application.

Another object of the present invention is to provide a servo motorwhich appreciably reduces the port hole cutting of the sealing cup usedtherein.

These and other objects and advantages will become apparent hereinafter.The present invention comprises a plurality of servo motors seriallyarranged with a positive displacement pressure producing means in ahydraulic system. The servo motors are manually operated therebyrestricting the pressure uid flow therethrough to establish a pressuredifferential. This pressure differential supplements the operatorapplied force and acts as a booster force to actuate the vehicle brakes,power steering, and the like. The servo )motor described hereinafterprovides safe operation of the brake assemblies before, during and aftera power failure; however, in the event of failure, the operator mustsupply all of the force required.

The invention valso consists in the parts and in the arrangements andcombinations of parts hereinafter described and claimed. In theaccompanying drawings which form part of this specication and hereinlike numerals and symbols refer to like parts wherever they occur:

FIG. 1 illustrates a braking system having a preferred embodiment ofthis invention therein shown partially in cross-section, and

FIG. 2 shows a modification of the preferred embodi- V ment partially incross-section in a braking system.

This is a continuation of co-pending application, Serial No. 496,711,-led March 28, 1955, now abandoned, for Power Hydraulic Brake Device.

As used herein, the term open center refers to a system defined ashaving a continuous pressure iiuid flow `or circulation `therein and adormant state characterized by a relatively small iluid pressurepotential. The term open center shall also refer to a valve or servomotor for controlling or functioning in such -a system, `and adapted tothrottle or restrict the ilow of pressure fluid therethrough to generateuid pressures in the system on the inlet side of the valve withoutappreciably diminishing theV volumetric rate of pressure uid flowthrough the system on both sides o-f the valve.

ice

The term ambient `as used in reference to fluid pressures in an opencenter system or servo motor shall mean the pressure of iiuid in thesystem across a servo motor imposed by a force or means of the systemexternal to the servo motor at any given instant.

Referring to FIG. 1, the power hydraulic system shown comprises apositive displacement pumping means 1 supplied by a iiuid reservoir 2through a conduit 3. The pressure side of the pumping means 1 isconnected by a conduit 4 to an inlet and an inlet chamber A in a servomotor 5. A conduit 6 connects the outlet side of the -motor 5 with apower hydraulic steering valve 7 arranged in series with said motor. Theoutlet of said steering valve 7 is connected with the reservoir 2 by aconduit 8 thus providing a return passage for the -tiuid displaced bythe pumping means 1.

In addition to the above circuit, `a conduit 9 is provided connectingthe conduits 6 `and 8 and having a reverse How valve 1t) interposedtherein, said reverse flow valve being employed to facilitate pressurefluid recirculation during a power steering failure application. Ifdesired, the valve 1u may be integral with the power steering valve 7. Apressure relief valve 11 is interposed in a conduit 12 which connectsthe conduits 3 and 4 and provides a shunt or by-pass around the pumpingmeans 1 thereby protecting said means from pressure overloads. Also aconduit 13 is connected between the reservoir 2 and a fluid port in theservo motor 5 for compensation purposes. A conduit 14 is attached to thepressure sidel of the servo motor 5 and leads to a plurality of wheelcylinders 15 which actuate the brake assemblies.

The servo motor 5 comprises a booster housing 16 having a brake housing17 secured to the right end thereof. The booster housing 16 has a pistonbore 18 and a counterbore 19 horizontally `arranged therein. Thecounterbore V19 is provided with a vertically positioned inlet 20 at itsleft end and an outlet 21 near the right end thereof. A ball typepressure relief valve 22 is interposed between inlet 20 and outlet 21being received in the connecting passage formed by a horizontal bore 23`and axially aligned counterbore 24, the valve 22 being biased against aseat 25 by a'valve spring 26 carried by a guide member 27. The right endof the spring 26 abuts against a sealing member 28 and has itscompressive force predetermined by a spacer 29 against which the rightside of the sealing member 2S is seated.

A power piston 30 is freely and slidably mounted in the bore 18 andcounterbore 19 and is provided with an enlarged portion 31 substantiallyat the mid-portion thereof carrying an O ring 62 to provide a sealbetween the wall of the counterbore 19 and the outer periphery of saidenlarged portion. Thus, the enlarged portion 31 of the power piston 30forms an inlet chamber A in the counterbore leftwardly thereof and amain chamber B rightwardly thereof. Another O ring 63, supported in agroove in the bore 1S seals a leftward extension 30 of the piston 30.Cross-drilled passageways 32 and 33 are positioned on opposite sides ofthe enlarged portion 31 and intersect a bore 34 within the piston 30.Slidably received in the bore 34 is a throttling rod 35 have acircumferential groove 36 in its mid-portion forming a throttlingpassage D and a channel 37 between said rod 35 and bore 34. An O ring 64is supported in the left end' of the rod 36 to provide a seal betweenthe bore 34 of the power piston 30 and the rod 35, and another O ring 65is supported in said rod 35 rightwardly of the groove 37 to provide aseal between the bore 34 and the rod 35. The leftward end of thethrottling rod 35 pivotally receives one end of a push rod 38. Aresilient boot 39 houses the leftward end's of the power pist-on 30 androd 34 outwardly of the seals 63 and 64, and the boot 39 prevents theentry of foreign matter into the servo motor associa 5 and is positionedbetween the left end of the servo motor 5 and the push rod 3S. Theleftward end of said push rod 38 is attached to a brake actuating pedal4f) through a mechanical linkage (not shown). The actuating pedal 4f) isprovided with a return spring (not shown) which exerts a positive, butnegligible, return or leftward force on the push rod 38 and throttlingrod 35.

The free and slidable power piston 3ft has a rightward projection orextension 30 of the same diameter as the leftward extension 30', theprojection extending coaxially into a working or outlet bore 41 providedin the brake or master cylinder housing 17 through a seaiing ring 42retained in the right end of the counterbore 19 by suitable means. Thebore 34 extends through the projection 30 and the right end of thethrottling rod 35 also projects into the bore 41 extending beyond thepiston projection 31) and carrying a snap ring which is seated in arecess 44 adjacent to the right end portion of the power pistonextension 30". The throttling rod 35 also carries a cup back-up washer45 and a double-lipped, resilient, sealing cup 46 which are positionedthereon by retaining means 47 secured to the rod 35. Since the rod 35 isurged leftwardly by the actuating pedal return spring (not shown), theretainer 47, the cup 46, the washer 45, and the right end or edge of thepiston extension 3Q are normally biased into an abutting relationship.

A reservoir port 4S is vertically positioned in the upper portion of thebrake housing 17 for compensation purposes. One end of the reservoirport e8 receives the conduit 13 and the other end intersects the bore 41adjacent to the lip of the cup 46 as shown. An outlet or pressureproducing chamber C is formed in the bore 41 rightwardly of the cup 46and is provided with an outlet port or brake port 49 which connects therightward end of the bore 41 with the conduit 14. A compensation valve50 is positioned between the reservoir port 48 and the brake port 49 andis mounted in a connecting passageway formed by a horizontal bore 51 andan axially aligned counterbore 52. The valve 50 is biased against a seat53 by a spring 54- positioned between said valve Sil and an end plug 55fxedly mounted in the counterbore 52. Another passageway 56 is angularlyinterposed between the reservoir port 48 and the bore 41 intermediatethe seals 42 and 46 and functions as a fluid supply port and lubricationmeans to connect the reservoir 2 with an annular groove 66 incommunication with the rightward end of the power piston extension 30".It is apparent that the pressure fluid' inthe outlet chamber C and inthe groove 66 is atmospheric in the normally inoperative position of theservo motor 5.

In this series flow system, the pressure relief valve 11 operates at apressure equal to the sum of the maximum pressure differentials allowedacross the individual servo motors and protects the pumping means 1 frompressure overloading which is caused when one or more of the servo`motors exceed the predetermined maximum pressure differential. Eachservo motor is provided with a pressure relief Valve which predeterminesthe maximum pressure differential allowed thereacross, and the fluidpressure developed by or existing in a servo motor at any time iseffective upon `every servo motor of prior position in the system. Ifthe steering valve 7 is actuated, the pressure differential createdtherein causes a back pressure which establishes the ambient Huidpressure in the servo motor 5 and against which the pumping means 1 mustwork. In the past a servo motor of prior position would be actuated bythis back pressure but, according to the present invention, the servomotor 5 is balanced to prevent such an occurrence.

Balacing is achieved by a symmetry of cross-sectional areas which areacted on by the ambient pressures in the system including the backpressure of the pressure fluid produced by means external of servo motor5 such as the valve 7. In the free and slidable piston 30, the effectivecross-sectional area of the leftward portion of the enlarged portion 31in the inlet chamber A is equal to the cross-sectional area of therightward portion which forms part of the main chamber B. This balancingmay also be seen as the substantially radial areas of the piston betweenthe sealing ring 62. and each of the sealing rings 63 and 42, or as theareas of the piston 3@ on which pressure fluid acts in the chambers Aand B between the seal 62 and the seals 63 and 42 sealing the extensions30 and 30 having equal diameters. In the throttling rod 35, the affectedcross-sectional area forming the leftward wall of the groove 36 isbalanced by an equal affected area forming the rightward wall thereof orthe areas of the rod 35 between the sealing rings 64 and 65. It is alsoapparent that the effective areas of the rod 35 and piston extensions 3Qand 311 outwardly of the seals 63, 64, 65 and 42 are acted on byatmospheric pressure and are substantially equal whereby these forcesare selfcancelling. 1n this manner, equal and opposite selfcancellingforces are produced on the piston 36 and rod 35 obviating the effect ofany back pressure imposed throughout the servo motor 5 in thatparticular section of the series flow system.

Assuming the steering valve 7 to be unrestricted, pressure fluid isnormally discharged from the pumping means 1 through the conduit 4 andthe inlet 2G into the inlet chamber A of the servo motor 5 where itfiows through passageway 32 unrestricted into the throttling passage Dand through the passageway 33 and therefrom into the counterbore 19 orchamber B. From the counterbore 19, the fluid flows through the outlet21 and the conduit 6 into the power steering valve 7 and is thenreturned to the reservoir 2 through the conduit 8.

When the vehicle operator applies a force to the actuating pedal 4), aproportional force is transmitted to the push rod 33 and the throttlingrod 35 through the intermediate linkage (not shown). Therefore, thethrottling rod- 35 is moved rightwardly restricting pressure fluid flowthrough the throttling passage D or the channel 37 thereby creating apressure differential across the enlarged portion 31 of the free andslidable piston 31E. Because of this pressure differential, the powerpiston 3ft moves rightwardly carrying the washer 45 and cup 46 furtherinto the pressure producing chamber C of the bore 41, and the throttlingrod 35 `necessarily follows and maintains the restriction of thethrottling passage D and the restriction of fluid through the channel 37because of the manually applied force. This movement displaces pressurefluid from the bore 41 or outlet chamber C to the brake port 49 and theconduit 14 into the wheel cylinders 15 thereby actuating the brakeassemblies. The magnitude of the maximum pressure differential ispredetermined by the operating or actuating pressure of the pressurerelief valve 22.. The fluid pressure developed in the outlet chamber Cacts on the effective areas 'of the washer 45 and the cup 46 vand alsothe rod 35 creating a reactionary force in opposition to the motivatingforce of `the piston 30 and the rod 35. When the reactionary forceequals the motivating force, the rightward movement of said piston 3f)and rod 35 ceases. Since the reactionary force thus created is effectiveupon the rod 35, the operator is afforded a direct feel as to the extentof the braking application.

When the operator releases the applied force, the es- -tablished fluidpressure in the bore 41 and the actuating pedal return spring returnsthe throttling rod 35, the free and slidable piston 3ft, and partsassociated therewith to their normal positions. When this occurs, apartial vacuum is developed in the bore 41. The compressive force of thespring 54 in association with the compensation valve 50 is very lightallowing the valve to be actuated at a very small pressure differentialexisting between the bore 51 and the bore 41. Thus, pressure fluid isallowed to flow past the valve 50 at a small pressure differential tocompensate for pressure fluid losses in the bore 41.

Since fluid compensation into chamber C is not accomplished bycollapsing the lip of sealing cup 46, saidsealing cup may be providedwith a shorter and stiffer lip portion so .that it will be exposed toport hole cutting for a vshorter distance and be more resistant to porthole cutting during said shorter distance.

In the event of la power failure, the operator is required to supply allof the actuating force to operate the servo motor 5. As previouslydescribed, the force applied by the operator moves the throttling rod 35rightwardly. Due to the absence of pressure fluid flow through thethrottling passage D, a pressure differential is not created to motivatethe free and slidable piston 30 and actuation of the pressure producingor working parts in the outlet chamber C occurs by manual movement ofthe throttling rod 35 only. The immobility of the piston 30 obviates theneed for a reverse flow valve between chambers A and B of the servomotor since displacement of pressure fluid from chamber B does not occurand seal `friction is not created. Therefore, the manually applied forcenormally required for a braking application after a power failure isreduced. Consequently, the throttling rod 35 carries the snap ring 43,the washer 45, and cup 46 into the ,bore 41 displacing pressure fluidfrom the outlet chamber C to the brake port 49 and the conduit 14 intothe wheel cylinders which actuate the ybrake assemblies. In this case,the force in opposition to the force of the pressure fluid in the bore41 acting lupon `the effective areas of the cup 46 and the rod 35 issupplied totally by the operator. Upon release of said applied force,`the fluid pressure in the bore 41 and the actuating pedal springreturns the throttling rod 35 and parts associated therewith to theirnormal positions.

A modification of the embodiment is illustrated in FIG. 2 wherein likenumeral-s and letters refer to like parts in lthe preferred embodimentwherever possible.

In the power hydraulic system, the pressure relief valve of the pumpingmeans 1 is omitted, and a pressure relief valve 57 is positioned in theconduit 9 across the steering valve 7. A conduit 58 connects the inletand outlet conduits 4 and 6 of the servo motor 5 and is provided with areverse flow valve 59 and a pressure relief valve 60 positioned therein.

The general arrangement of the servo motor 5 remains substantially thesame except that an abutment 61 is provided on the left end of the rod35 instead of the snap ring 43 carried by the rod 35 in the FIG, lembodiment. The operation of the servo motor 5, FIG. 2, also remainssubstantially the same except during a power failure application. WhenIthe operator applies a force -to the actuating pedal 40 during a powerfailure, the force is transmitted, as previously described, motivatingthe rod 35 rightwardly. Due to the absence of pressure fluid flowthrough the channel 37, a pressure fluid differential resulting fromthrottling the passage D is not created to motivate the piston 30.Consequently, the abutment 61 engages and moves the piston 30rightwardly. The right end of the piston 30 carries the washer 45 andthe cup 46 into the bore 41 and outlet chamber C displacing pressurefluid therefrom through the brake port 49 and conduit 14 into the wheelcylinders 15 which actuate the brake assemblies. In this oase, thereverse flow valve 59 is necessitated for the recirculation of thepressure fluid displaced displaced from the chamber B by the piston 30.Upon the release of the applied force, the fluid pressure in the bore 41and the actuating pedal spring returns the rod 35, the piston 30, andparts associated therewith to their normal positions.

This invention is intended to cover all changes and modifications of theexample of the invention herein chosen for purposes of the disclosure,which do not con'- stitute departures from the spirit and scope of theinvention.

vWhat we claim is:

1. A servo motor for an open center fluid pressure system having pumpingmeans for continuously circulating pressure fluid through said systemand said servo motor, said servo motor comprising a cylinder, inlet andoutlet ports in said cylinder connected with the discharge and returnsides, respectively, of said pumping means, a power piston slidable insaid cylinder between said inlet and outlet ports, extension means onsaid power piston extending externally of said cylinder, said powerpiston having a bore and inlet and outlet passage means on oppositesides of said power piston providing fluid communication between saidbore and said inlet and outlet ports, a` throttling rod slidable in saidbore, said throttling rod and power piston forming a throttling passagetherebetween in communication with said inlet and outlet passage meansin said power piston providing series pressure fluid llow from saidinlet port to said outlet port, cooperable means on said throttling rodand power piston forming a normally unrestricted, but variable valvingorifice in said throttling passage, said throttling rod being movablerelative to said power piston in response to an applied force to reducethe size of the variable valving orifice for developing a fluid pressuredifferential across said power piston to actuate said power piston andextension means in follow-up relation with said throttling rod and tomaintain said valving orifice in a non-closed condition for continuouscirculation of pressure fluid therethrough.

2. The servo motor according to claim l, wherein the opposing effectiveareas of each of said rod and power piston, respectively, in saidcylinder are susbtantially equal and are acted on by ambient fluidpressure of the system.

3. The servo motor according to claim 2, wherein ambient fluid pressureis effective through said cylinder on the inlet and outlet port sides ofsaid power piston and in said throttling passage and inlet and outletpassages, whereby the forces produced by the ambient fluid pressure ofthe system` acting on the opposing effective areas of each of saidthrottling rod and power pistons are selfcanceling.

4. The servo motor according to claim 4, including a pressure producingchamber coaxially disposed at one end of said chamber, and wherein saidextension means includes a first extension with a working end positionedin said pressure producing chamber, a second extension on said powerpiston extending in an opposite direction from said rst extension andhaving an end positioned out of said cylinder, said extensions being ofthe same diameter, and sealing means between said power piston and saidcylinder and between said extensions and said cylinder.

5. The servo motor according to claim 4, wherein said throttling rod isslidable in said bore and has a first end in said pressure producingchamber and a second end positioned out of said cylinder, said powerpiston and throttling rod, respectively, having substantially equalopposed pressure responsive areas acted on by the ambient fluid pressureof said system, and the ends of said throttling rod and the ends of saidfirst and second extensions, respectively, having substantially equalopposed effective areas normally acted on by atmospheric pressure out ofsaid cylinder and in said chamber.

6. The servo motor according to claim 5, wherein piston means areprovided in said pressure producing chamber in position to be actuatedby the Working end of said first extension, and lost motion connectionmeans between said throttling rod and said piston means in said pressureproducing chamber for actuation of the latter in response to an appliedforce on the throttling rod in the event of loss of pressure fluidcirculation from said pumping means.

7. The servo motor according to claim l, in which said servo motorincludes means for effecting concert movement of said power piston andthrottling rod in response to an applied force on the latter in theevent of loss of pressure fluid circulation from said pumping means, anda normally closed check valve between said inlet and outlet ports, saidcheck valve being opened by pressure fluid displaced from said cylinderthrough said outlet port upon the concert movement of said power pistonand throttling rod to return the displaced pressure fluid to saidcylinder through said inlet port.

8. An open center hydraulic circulating system comprising a pump, supplyand return lines connected to said pump, and at least two servo motorsin series flow relation between said supply and return lines, theoperation of each of said servo motors creating back pressures in saidsupply line, one of said servo motors comprising a power cylinder and apressure producing chamber, a slidable power piston dividing saidcylinder to form an inlet chamber connected by said supply line to saidpump and an outlet chamber connected to the other of said servo motors,said power piston having a Working end positioned in said pressureproducing chamber, the opposing effective areas of said power piston incommunication with said inlet and outlet chambers being substantiallyequal to prevent movement of said power piston in response to the backpressure in said system imposed across said one servo motor `by saidother servo motor, said power piston having a bore and inlet and outletpassage means on opposite sides of said power piston providing fluidcommunication between said bore and said inlet and outlet chambers, a

throttling rod slidable in said bore, said throttling rod 'and powerpiston forming a throttling passage therebetween in communication withsaid inlet and outlet passage means in said power piston providingseries pressure fluid tlow from said inlet port to said outlet port,cooperable means on said throttling rod and power piston forming anormally unrestricted, but variable valving orice in said throttlingpassage, said throttling rod being movable relative to said power pistonin response to an applied force to reduce the size of the variablevalving orifice for developing a iiuid pressure diierential across saidpower piston to actuate said power piston and extension means infollow-up relation with said throttling rod and to maintain said valvingorice in a non-closed condition for continuous circulation of pressureriluid therethrough.

9. The system according to claim 8, wherein said power piston of saidone servo motor includes a first extension having said working endpositioned in said pressure producing chamber, a second extension onsaid power piston extending in an opposite direction from said rstextension and having an end positioned out of said cylinder, theopposing elective areas of said extensions being substantially equal,and sealing means between said power piston and said cylinder andbetween said extensions and said cylinder.

10. The system according to claim 9, wherein said throttling rod of saidone servo motor has a rst end in said pressure producing chamber and asecond end positioned out of said cylinder, said power piston andthrottling rod, respectively, having substantially equal opposedpressure responsive areas acted on by the ambient fluid pressure of saidsystem, and the ends of said throttling rod and the ends of said firstand second extensions, respectively, having substantially equal opposedeffective areas normally acted on by atmospheric pressure out of saidcylinder and in said pressure producing chamber.

11. The system according to claim 8, whereinV said one servo motorincludes piston means provided in said pressure producing chamber inposition to be actuated by the working end of said power piston, andlost motion connection means between said throttling rod and said pistonmeans in said pressure producing chamber for actuation or the latter inresponse to an applied force on the throttling rod in the event of lossof pressure uid circulation from said pumping means.

12. The system according to claim 8, in which said one servo motorincludes means for eiecting concert movement of said power piston andthrottling rod in response to an applied force on the latter in theevent of loss of pressure uid circulation from said pumping means, and anormally closed check valve connected in parallel relation with saidpumping means ybetween said inlet and outlet ports, said check valveIbeing opened by pressure uid displaced from said cylinder through saidoutlet port upon the concert movement of said power piston andthrottling rod to return the displaced pressure fluid to said cylinderthrough said inlet port.

13. The system according to claim 11, wherein said throttling rod isimperforate and has one end positioned in said pressure producingchamber, and retaining means k carried by said one end of saidthrottling rod for engaging and returning said piston means to itsnormally inoperative position in said pressure producing chamber.

References Cited in the file of this patent UNITED STATES PATENTS1,890,010- Vickers Dec. 6, 1932 1,960,996 Guernsey May 29, 19342,059,082 Brady et ai oct.` 27, 1936 2,517,005 MacDuft Aug. 1, 19502,624,361 Brown Jan. 6, 1953 2,844,941 Ayers July 29, 1958 UNITED STATESPATENT oEEICE CERTIFICATE 0F CORRECTIGN Patent No 3,0509l4 August 28l962 Robert Eo Schwartz et al.

It is hereh;T certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below'.

Column 2E line 60, for have read having -g column 3,E line 6C) for"Balaciug" read Balancing column 6u line 36 for the claim referencenumeral "4" read l Signed and sealed this 22nd day of January 19634u(SEAL) Attest:

VERNEST w. swIDER DAVID L. LADD Attesting Offieer Commissioner ofPatents

